Rolling back r10049 due to webkit failures.

src/ia32/codegen-ia32.cc

Index: src/ia32/codegen-ia32.cc
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index d325938eb0cb0a55e38a44280c8e79852b528b10..58eead772b067f9c5f550b0b53b2d18ba9d90f92 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -563,17 +563,15 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
     __ Assert(zero, "external string expected, but not found");
   }
   __ mov(result, FieldOperand(string, ExternalString::kResourceDataOffset));
+  // Assert that the external string has not been finalized yet.
+  __ test(result, result);
+  __ j(zero, call_runtime);
   Register scratch = string;
   __ mov(scratch, FieldOperand(string, HeapObject::kMapOffset));
-  __ movzx_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
-  // Rule out short external strings.
-  STATIC_CHECK(kShortExternalStringTag != 0);
-  __ test_b(scratch, kShortExternalStringMask);
-  __ j(not_zero, call_runtime);
-  // Check encoding.
-  STATIC_ASSERT(kTwoByteStringTag == 0);
-  __ test_b(scratch, kStringEncodingMask);
-  __ j(not_equal, &ascii_external, Label::kNear);
+  __ cmp(scratch, Immediate(factory->external_ascii_string_map()));
+  __ j(equal, &ascii_external, Label::kNear);
+  __ cmp(scratch, Immediate(factory->external_ascii_symbol_map()));
+  __ j(equal, &ascii_external, Label::kNear);
   // Two-byte string.
   __ movzx_w(result, Operand(result, index, times_2, 0));
   __ jmp(&done);